Edge enhancement depletion technique for over-sized ink drops to achieve high resolution X/Y axes addressability in injet printing

ABSTRACT

A swath printing system such as multi-color inkjet printing which uses lower resolution printheads of at least 300 dpi nozzle spacing to achieve high resolution output of at least 600 dpi addressability in both the X (media advance) and Y (carriage scan) axes. Synchronized depletion masks for area fills and edge enhancement is provided which is plot independent and prevents drop overlap. It is especially suited for multi-pass print modes since each row has a balanced number of pixels, and there are no rows which have no “on” pixels. The depletion includes separate depletion masks and rules for edge enhancement as compared to area fills. Each color plane is depleted separately, but subject to the same depletion rules and masks. A separate depletion step provides for narrowing the vertical and horizontal dimensions of the figure to be printed.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation/divisional of U.S. Ser. No.08/734,324 filed Oct. 21, 1991 by Victor Alfaro, now U.S. Pat. No.6,296,343 incorporated herein by reference.

This application is related to the following applications which are allassigned to the assignee of the present invention, and which are allincorporated herein by reference: U.S. Ser. No. 08/734,326 filed Oct.21, 1996 by Victor Alfaro entitled COLOR INKJET DEPLETION TECHNIQUE FOROVER-SIZED INK DROPS TO ACHIEVE HIGH RESOLUTION X/Y AXES ADDRESSABILITY,now U.S. Pat. No. 6,299,284; U.S. Ser. No. 08/734,227 filed Oct. 21,1996 by Victor Alfaro entitled EXTERNAL DIMENSION INTEGRITY FOR HIGHRESOLUTION ADDRESSABILITY IN COLOR INKJET PRINTING; U.S. Ser. No.08/731,814 filed Oct. 21, 1996 by Alex Roche, Jordi Gonzalez, VictorAlfaro, Carlos Miranda, and Cristina Estabillo entitled MULTI-COLORSWATH PRINTING USING LOWER RESOLUTION INKJET PRINTHEADS TO ACHIEVE HIGHRESOLUTION X/Y AXES ADDRESSABILITY; U.S. Ser. No. 08/731,815 filed Oct.21, 1996 entitled PLOT-INDEPENDENT AREA FILL DEPLETION TECHNIQUE FORHIGH RESOLUTION X/Y AXES ADDRESSABILITY IN INKJET PRINTING.

BACKGROUND OF THE INVENTION

This invention relates generally to swath printing, and moreparticularly to inkjet printers using separate nozzle arrays for eachdifferent color ink.

While much research and development has been directed toward increasingthe nozzle resolution on inkjet printheads as the best way to improveprint quality, some benefits can also be obtained through print modetechniques. Higher resolution addressability has already been obtainedto some degree with monochrome print mode techniques. Examples of thisare found in U.S. Pat. No. 5,541,625 issued Jul. 30, 1996 for METHOD FORINCREASED PRINT RESOLUTION IN THE CARRIAGE SCAN AXIS OF AN INKJETPRINTER; U.S. Pat. No. 5,469,198 issued Nov. 21, 1995 entitled MULTIPLEPASS PRINTING FOR ACHIEVING INCREASED PRINT RESOLUTION; and U.S. Pat.No. 5,535,307 issued Jul. 9, 1996 entitled PRINTING OF VARIABLE DOTSIZES DEPENDENT UPON IMAGE DENSITY FOR IMPROVED GRAPHICS.

The monochrome techniques for increased addressable resolution, and therelated depletion techniques, are not easy to apply to color printing,particularly where the goal is to have increased resolution in both theX and Y axes (media advance and carriage scan axes, respectively) asgenerally labeled for wide format printers/plotters.

An increased color resolution printer from Epson was introduced whichprovided some color depletion after increasing addressable resolution to720×720. This product was unfortunately based on a very low nozzleresolution printhead of 90 dpi, which required a slow tedious eight passprint mode as well as special media to decrease ink dot gain.

So there still remains a need for a faster increased resolution higherresolution print technique which includes improved dot depletion toassure better print quality for a wider selection of media.

BRIEF SUMMARY OF THE INVENTION

The invention provides a swath printing system such as multi-colorinkjet printing which uses lower resolution printheads of at least 300dpi nozzle spacing to achieve high resolution output of at least 600 dpiaddressability in both the X (media advance) and Y (carriage scan) axes.

Increased resolution is achieved in the X axis in a first embodiment byprinting on a first carriage pass a first set of color ink drops onto afirst group of pixel rows spaced apart at the lower resolution distance(e.g., 1/300 inch) and extending longitudinally in the Y axis direction,advancing the media to re-position the nozzles, and then printing on asecond carriage pass a second set of ink drops onto a second group ofdifferent pixel rows also spaced apart at the lower resolution distanceand extending longitudinally in the Y axis direction, with the secondgroup of pixel rows interlaced between the first group of pixel rows. Arelated feature of the invention is to advance the media in a preferredfour pass print mode, with even and odd numbered pixel rows beingprinted on alternate swaths based on advancing the media differentdistances between each swath.

A second embodiment provides increased resolution in the X axis by theoffset positioning of two printheads of the same color ink with theirrespective nozzles mis-aligned in the Y axis direction so that both theaforesaid first and second group of interlaced pixel rows can be printedon the same carriage pass, the first group by nozzles of one printheadand the second group by nozzles of the other.

Increased resolution is provided in the Y axis in a first embodimenthaving a single printhead for each color by any of the following:

1) maintaining the same carriage speed and the same firing frequency forthe printhead, and printing on a first carriage pass a first set ofcolor drops onto a first group of pixel columns spaced apart at thelower resolution distance (e.g., 1/300 inch) and extending in the X axisdirection, and then printing on a second carriage pass a second set ofink drops onto a second group of different pixel columns also spacedapart at the lower resolution distance and extending in the X axisdirection, with the second group of pixel columns interlaced between thefirst group of pixel columns;

2) maintaining the same carriage speed but doubling the firing frequencyfor the printhead, so that both the aforesaid first and second group ofinterlaced pixel columns can be printed on the same carriage pass; or

3) moving the carriage at half the usual speed, but maintaining the samefiring frequency for the printhead, so that both the aforesaid first andsecond group of interlaced pixel columns can be printed on the samecarriage pass.

Increased resolution is provided in the Y axis in a second embodiment byhaving two printheads for each color offset in the X axis direction sothat both the aforesaid first and second group of interlaced pixel rowscan be printed on the same carriage swath.

A further feature of the invention is the use of a plot-independentdepletion mask for area fills which improves print quality.

Synchronized depletion masks for area fills and edge enhancement areprovided which are plot independent and prevent drop overlap. It isespecially suited for multi-pass print modes since each row has abalanced number of pixels, and there are no rows which have no “on”pixels. The depletion includes separate depletion masks and rules foredge enhancement as compared to area fills. Each color plane is depletedseparately, but subject to the same depletion rules and masks. Aseparate depletion step provides for narrowing the vertical andhorizontal dimensions of the figure to be printed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a large format inkjet printer/plottercapable of incorporating the features of the present invention;

FIG. 1B is a close-up view of the carriage mechanism of theprinter/plotter of FIG. 1A;

FIG. 2 shows a presently preferred embodiment of a print cartridgearrangement in a scanning carriage wherein four separate printcartridges for yellow, cyan, magenta and black ink can be utilized togenerate higher resolution X/Y axis addressability from lower resolutionprintheads;

FIG. 3 shows another embodiment of a print cartridge arrangement in ascanning carriage where one separate print cartridge for black ink alongwith a tri-compartment print cartridge for cyan, magenta, and yellow inkcan be utilized to generate the higher resolution addressability of theinvention;

FIG. 4 shows an additional embodiment of a print cartridge arrangementin a scanning carriage where a first tri-compartment print cartridge foryellow, light magenta, and dark magenta ink along with a secondtri-compartment print cartridge for black, light and dark cyan ink canbe utilized to generate the higher resolution addressability of theinvention;

FIG. 5 shows an additional embodiment of a print cartridge arrangementin a scanning carriage where two separate print cartridges for each ofyellow, cyan, magenta and black inks can be utilized to generate thehigher resolution addressability of the invention;

FIG. 6 shows a further embodiment of printhead arrangements in ascanning carriage wherein four separate cartridges for different inkcolors which are staggered to provide non-overlapping swaths for eachcolor can be utilized to generate the higher resolution addressabilityof the invention;

FIG. 7 shows yet another embodiment of a tri-compartment printheadwherein three separate nozzle arrays for different ink colors such asyellow, cyan, and magenta which are staggered to provide non-overlappingswaths for each color can be utilized to generate the higher resolutionaddressability of the invention;

FIG. 8 shows still a further embodiment of a tri-compartment printheadwherein three separate nozzle arrays for different ink colors such asblack, light cyan, and dark cyan which are aligned to provideoverlapping swaths for each color can be utilized to generate the higherresolution addressability of the invention;

FIG. 9 shows a different embodiment of two separate printheads of agiven nozzle resolution such as 300 dpi both having the same color ofink, and being relatively positioned on a scanning carriage to have asmall nozzle overlap with no direct nozzle alignment in the direction ofthe Y axis;

FIG. 10 shows the printheads of FIG. 9 being relatively positioned on ascanning carriage to have approximately 50% nozzle overlap;

FIG. 11 shows the printheads of FIG. 9 being relatively positioned on ascanning carriage to have almost 100% nozzle overlap;

FIG. 12 is a schematic drawing showing a comparison between thetheoretical drop size and the actual drop size for typical 300 dpi and600 dpi ink drops;

FIG. 13 shows an area fill depletion mask of the present invention whichcan be used when oversized color ink drops are applied to an increasedresolution addressable grid;

FIG. 14 is a schematic drawing showing four virtually identical 300 dpinozzle arrays as used in the print cartridge arrangement of FIG. 2;

FIG. 15 shows a presently preferred embodiment of a multipass print maskof the present invention as used with the area fill depletion mask ofFIG. 13;

FIG. 16 is a schematic drawing showing the amount of media advance for afour-pass increased resolution addressable print mode of the presentinvention;

FIG. 17 is an enlarged schematic representation showing and area fill ofmagenta ink made with the print masks of FIGS. 13 and 15 for 300 dpidrops on a 600×600 addressable grid, as compared to an area fill ofblack ink made with undepleted 600 dpi drops on the same 600×600addressable grid;

FIGS. 18-19 are self explanatory flow charts showing the depletiontechniques of the invention;

FIGS. 20 and 21 show the depletion masks for horizontal and verticaledges, respectively;

FIG. 22 is a comparison of lines made with 600 dpi size non-dropsdepleted drops and 300 dpi size depleted drops on a 600×600 dpi grid;

FIG. 23 shows the 300 dpi dot size on a 600×600 dpi grid;

FIGS. 24-29 are self-explanatory schematic representations of thevarious steps of the depletion techniques of the invention;

FIG. 30 is a self-explanatory flow chart for the representations ofFIGS. 24-29; and

FIGS. 31 and 32 show a thickened line on a 600×600 dpi grid before andafter depletion, respectively.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

A typical embodiment of the invention is exemplified in a large formatcolor inkjet printer/plotter as shown in FIGS. 1A-1B. More specifically,FIG. 1A is a perspective view of an inkjet printer/plotter 210 having ahousing 212 mounted on a stand 214. The housing has left and right drivemechanism enclosures 216, 218. A control panel 220 is mounted on theright enclosure 218. A carriage assembly 300, illustrated in phantomunder a cover 222, is adapted for reciprocal motion along a carriage bar224, also shown in phantom. The position of the carriage assembly 300 ina horizontal or carriage scan axis is determined by a carriagepositioning mechanism 310 with respect to an encoder strip 320 (see FIG.1B). A print medium 330 such as paper is positioned along a vertical ormedia axis by a media axis drive mechanism (not shown). As used hereingthe media axis is called the X axis denoted as 201, and the carriagescan axis is called the Y axis denoted as 301.

FIG. 1B is a perspective view of the carriage assembly 300, the carriagepositioning mechanism 310 and the encoder strip 320. The carriagepositioning mechanism 310 includes a carriage position motor 312 whichhas a shaft 314 which drives a belt 324 which is secured by idler 326and which is attached to the carriage 300.

The position of the carriage assembly in the scan axis is determinedprecisely by the encoder strip 320. The encoder strip 320 is secured bya first stanchion 328 on one end and a second stanchion 329 on the otherend. An optical read 366 is disposed on the carriage assembly andprovides carriage position signals which are utilized by the inventionto achieve optimal image registration in the manner described below.

Referring to FIG. 2, a carriage 102 is slidably mounted on support bar172 through a bearing sleeve 171, and includes four slots 121, 123, 125,127 for removably receiving four.inkjet print cartridges. From right toleft in the carriage slots are respectively mounted a black inkcartridge 120, a magenta ink cartridge 122, a cyan ink cartridge 124 anda yellow ink cartridge 126. Although the invention has been successfullydemonstrated with four 300 dpi print cartridges of the type shown inFIG. 2 (see also FIG. 14), in a currently preferred embodiment the blackink cartridge has a 600 dpi nozzle resolution and therefore prints 600dpi sized drops which require no depletion (see the area fill comparisonin FIG. 17).

Referring to FIG. 3, a modified carriage 102 a carries a removablymounted black ink cartridge 130, and a tri-compartment ink cartridge 132which has separate ink reservoirs 133, 134, 136 for cyan, magenta andyellow ink, respectively.

Referring to FIG. 4, a further modified carriage 102 b carries a firsttri-compartment ink cartridge 140 which has separate ink reservoirs 142,144, 146 for yellow, light magenta, and dark magenta ink, respectively.A second adjacent tri-compartment ink cartridge 150 has separate inkreservoirs 152, 154, 156 for black, light cyan, and dark cyan ink,respectively.

Referring to FIG. 5, another modified carriage 102 c has a plurality ofindividual mounting slots 158 for carrying two adjacent yellow inkcartridges 160, 161, two adjacent cyan ink cartridges 162, 163, twoadjacent magenta ink cartridges 164, 165, and two adjacent black inkcartridges 166, 167,

Referring to FIG. 6, a different arrangement of staggered color inkprintheads C1, C2, C3 and C4 are shown for cyan, magenta, yellow andblack ink, respectively. The cartridge C4 can be aligned with either themagenta or cyan cartridge, or can be separately positioned at position168 to be non-overlapping with the other print cartridges. The nozzleresolution P1 can be the same as P2 as shown in the drawing (e.g. 300dpi), or can be 600 dpi (not shown in this drawing).

The tri-compartment nozzle plate 175 in FIG. 7 shows three nozzle arrays176, 177, 178 for yellow, cyan, and magenta ink, respectively, which arestaggered in order to print separate swaths during a single pass. Thetri-compartment nozzle plate 180 in FIG. 8 shows three nozzle arrays181, 182, 183 for black, light cyan, and dark cyan ink, respectively.

FIGS. 9 and 10 show two identical 300 dpi printheads 185, 186 for thesame color ink being positioned in different overlapping nozzlepositions, but with no direct alignment in the Y axis direction betweenany nozzles in either printhead. This enables the possibility ofprinting on pixel rows which are 1/600th inch apart on a single carriagepass. The schematic of FIG. 11 shows the relationship between a nozzlepitch 188 of the 300 dpi for adjacent nozzles on the same printhead, ascompared to a nozzle pitch 189 of 600 dpi for adjacent nozzles ondifferent printheads.

The non-aligned nozzles of FIGS. 9, 10 and 11 are contrasted with thealigned nozzles of the four identical 300 dpi printheads 190, 191, 192,193 of FIG. 14. By printing with only 48 of the 50 nozzles, theremaining nozzles at one end or the other of the printhead can be turned“off” in order to facilitat the best possible alignment (see arrows 195,196). The printhead arrangement of FIG. 14 has been implemented incombination with the area fill depletion mask 197 in FIG. 13 in order toprint the depleted area fill of magenta drops schematically shown inFIG. 17.

The schematic drawing of FIG. 12 shows the size difference betweentheoretical and actual ink drops for a 300×300 dpi grid, as well as fora 600×600 dpi grid. The problem of too much ink is especially magnifiedwhen printing 300 dpi size ink drops on a 600×600 dpi grid. For thisreason, it is very desirable to develop an improved depletion mask.Prior monochrome depletion techniques often provided inconsistentresults because they were based in part on the external shape of afigure to be printed. In contrast, the present invention provides a plotindependent mask as shown in FIG. 13. This is the basic grid which ispreferably used for area fills, and it extends over the entire plot areato provide unique synchronized depletion. There is no drop overlap andthis depletion mask has pixels “on” in every row. Both even and odd rowshave 25% of the original amount of ink prior to depletion, so thatinterleaving print modes will work in a perfectly balanced way.Moreover, this depletion mask follows the periodic “on/off” firing mask197 which enables the printheads to maintain the same firing frequency(approximately 5.5 KHertz) while at the same time maintaining the samescanning speed for the carriage (approximately 18.33 inches/sec.).

In that regard, the four-pass cluster mode shown in FIG. 15 increasesprint quality and provides improved optical density. It is related tothe media advance shown in FIG. 16 wherein the printheads alternatebetween printing on even and odd numbered rows (49 rows, 47 rows, etc.).

It will be understood that the various arrangements and embodiments ofcolor printheads shown in the drawings can all be used to achieve thebenefits of the increased 600×600 addressable print modes of the presentinvention, all without the need for an excessive number of nozzle passesover the same printing area on the media.

It will further be understood that the synchronized depletion maskassures balanced and predictable ink depletion, independent of the shapeor color configuration of the figure(s) to be printed, thereby improvingcolor print quality.

FIGS. 18-19 show the separation of figures into separate color planesbefore depletion, and also show the separate depletion techniquesapplied to area fills as compared to edge enhancement.

The horizontal edge depletion mask of FIG. 20 shows the locations 206for the area fill “on” pixels, and the vertical edge depletion mask ofFIG. 21 also shows such locations 207.

The non-depleted pixel separations in FIG. 22 are shown at 208, while adepleted pixel separation is shown at 209.

Dot next to dot secondary colors 213, 215 as well as dot on dotsecondary colors 217 are shown in FIG. 23, on a 600×600 dpi grid, bothpresent problems of excessive ink.

The illustrative drawings of FIGS. 24-29 show what happens when all the.depletion rules and masks are applied to a figure, and the flow chart ofFIG. 30 is a self-explanatory sequential step by step visual explanationthereof.

Finally, the drawings of FIGS. 31 and 32 show how the depletiontechniques are applied to a thickened line.

While exemplary and preferred embodiments of the invention have beenshown and described, it will be appreciated by those skilled in the artthat various modification and revisions can be made without departingfrom the spirit and scope of the invention as set forth in the followingclaims.

I claim as my invention:
 1. A swath printing system where a scanningcarriage carries printheads along a carriage scan axis over media whichis periodically advanced through a print zone in a media advance axisdirection, comprising a plurality of printheads providing different inkcolours for application of different colour ink drops to a given outputon the media, each printhead including an active nozzle swath width anda given nozzle resolution based on the distance separating adjacentnozzles as measured along the direction of a media advance axis; mediaadvance means for moving the media in the media advance directionthrough the print zone a predetermined distance after completion of aprinting swath by the carriage in the direction of the scan axis; anddepletion means operable to narrow the given output by removing orshifting portions of an edge of a figure in order to minimizeundesirable changes to the size of the figure to be printed.
 2. Theswath printing system of claim 1 wherein said depletion techniqueincludes a depletion mask which narrows the vertical or horizontaldimension of a figure by a distance of at least one addressable pixel.3. The swath printing system of claim 1 which includes an addressablepixel grid having a higher resolution in at least one axis as comparedto said given nozzle resolution.
 4. The swath printing system of claim 3which includes an addressable pixel grid having a higher resolution inboth said media advance axis and said scan axis as compared to saidgiven nozzle resolution.
 5. The swath printing system of claim 3 whereinsaid addressable pixel grid has a higher resolution which is a multipleof said given nozzle resolution.
 6. The swath printing system of claim 3wherein said addressable pixel grid has a higher resolution which is atleast 600 dpi.
 7. A swath printing system where a scanning carriagecarries printheads along a carriage scan axis over media which isperiodically advanced through a print zone in a media advance direction,comprising: a plurality of printheads providing different ink coloursfor application of different colour ink drops to a given output on themedia, each printhead including an active nozzle swath width and a givennozzle resolution based on the distance separating adjacent nozzles asmeasured along the media advance direction; media advance means formoving the media in the media advance direction through the print zone apredetermined distance after completion of a printing swath by thecarriage in the direction of the scan axis; and depletion means operableto remove portions of an edge of a figure in order to minimize changesto the size of the figure to be printed, including a depletion maskwhich narrows the vertical dimension of a figure by a distance of atleast one addressable pixel; and wherein said depletion mask verticallyshifts only one horizontal edge of a figure by a distance of at leastone addressable pixel.
 8. A The swath printing system of claim 7 whereinsaid depletion mask does not shift a horizontal edge of a figure whenboth bottom and top horizontal edges constitute the same pixels.
 9. Aswath printing system where a scanning carriage carries printheads alonga carriage scan axis over media which is periodically advanced through aprint zone in a media advance direction, comprising: a plurality ofprintheads providing different ink colours for application of differentcolour ink drops to a given output on the media, each printheadincluding an active nozzle swath width and a given nozzle resolutionbased on the distance separating adjacent nozzles as measured along themedia advance direction; media advance means for moving the media in themedia advance direction through the print zone a predetermined distanceafter completion of a printing swath by the carriage in the direction ofthe scan axis; and depletion means operable to remove portions of anedge of a figure in order to minimize changes to the size of the figureto be printed, including a depletion mask which narrows the horizontaldimension of a figure by a distance of at least one addressable pixel.10. The swath printing system of claim 9 wherein said depletion maskhorizontally shifts only one vertical edge of a figure by a distance ofat least one addressable pixel.
 11. The swath printing system of claim10 where said depletion mask does not shift a vertical edge of saidfigure when both right and left vertical edges constitute the samepixels.
 12. A method of controlling external dimensions of a figureprinted with large ink drops which extend outside the boundaries ofindividual pixels on an addressable pixel grid by an inkjet printer,comprising detecting a horizontal edge of the figure; shiftingvertically certain selected pixels which form such horizontal edge inorder to narrow the outer dimensions of the figure, detecting one of theright or left edges of the figure; and shifting horizontally certainselected pixels which form such right or left edges in order to narrowthe outer dimensions of the figure.
 13. The method of claim 12 whereinsaid figure is formed by different coloured ink drops by an inkjetprinter, and further including the steps of: separating the figure intoa plurality of different colour planes corresponding to the differentcoloured ink drops; and applying said detecting and shifting stepsindependently to each different colour plane.
 14. The method of claim 12which further includes depleting any interior area fill portion of thefigure after having completed said detecting and shifting steps.
 15. Themethod of claim 12 which further includes detecting both horizontaledges of the figure, and not shifting any pixel which forms top andbottom horizontal edges at the same time.
 16. The method of claim 12which further includes detecting both vertical edges of the figure, andnot shifting any pixel which forms right and left vertical edges at thesame time.